Contents
Why is text between backticks called command substitution?
Text between backticks is executed and replaced by the output of the command (minus the trailing newline characters, and beware that shell behaviors vary when there are NUL characters in the output). That is called command substitution because it is substituted with the output of the command.
Why does Bash say backtick is not a command?
The backtick does exactly what you say it does. You have set a variable to an integer. When you put that variable inside backticks, bash will try to execute it as a command. Since it is not a command, you get the error you saw.
How to print 5 using backticks in Bash?
So if you want to print 5, you can’t use backticks, you can use quotation marks, like echo “$b” or just drop any quotation and use echo $b. As you can see, since $b contains 5, when using backticks bash is trying to run command 5 and since there is no such command, it fails with error message.
How to split a list of filenames in Bash?
It’s just a byte stream. The command inside the “ or $ () outputs a stream, which bash swallows and treats as a single string. As that point, you only have two choices: put it in quotes, to keep it as one string, or put it naked, so that bash splits it up according to its configured behavior.
What does a backtick mean in a shell?
A backtick is not a quotation sign. It has a very special meaning. Everything you type between backticks is evaluated (executed) by the shell before the main command (like chown in your examples), and the output of that execution is used by that command, just as if you’d type that output at that place in the command line.
Where are the backticks printed on the command line?
If you run this on the command line you get the following on the screen: Two lines are printed to STDOUT and one line to STDERR, but on the command line you can’t tell them apart. (You could use SCALAR and LIST context if you’d like to know the distinction.) The STDERR will be printed directly to the screen untouched by the backticks.
When to use a backtick or backward quote?
Since the use of the backward quote (Formally, a ?grave?, pronounced Gra-vee) or backtick has been mentioned, this is probably a good time to explain the rules regarding the use of quotes: * Double quote (?): Variables are expanded when enclosed in double quotes